1. Field of the Invention
The present invention relates to ink jet printing methods and apparatuses.
More particularly, the present invention relates to methods and apparatuses for the reduction of intercolor bleed, dry time, and smear by applying vacuum to print substrates during ink jet printing. In addition, it also relates to fast speed multi-color ink jet printing process for obtaining high quality images on plain papers.
2. Description of the Related Art
Ink jet printing is a non-impact printing method which produces droplets of ink that are deposited on a print substrate such as paper or transparent film in response to an electronic digital data signal. Thermal or bubble jet drop-on-demand ink jet printers have found broad application as output for personal computers in office and home.
Ink jet printing systems (apparatuses) generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at one orifice or nozzle. Multiple orifices or nozzles also may be used to increase imaging speed and throughput. The ink is ejected out of orifice and perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break up point, the electrically charged ink droplets are passed through an applied electrode which is controlled and switched on and off according with the digital data signals. Charged ink droplets are passed through a controllable electric field, which adjusts the trajectory of each droplet in order to direct it either to a gutter for ink deletion and recirculation or a specific location on a recording medium (print substrate) to create images. The image creation is controlled by electronic signals.
In drop-on demand ink jet systems, a droplet is ejected from an orifice directly to a position on a recording medium or a print substrate by pressure created by, for example, a piezoelectric device, an acoustic device, or a thermal ink jet devices controlled in accordance with digital signals. An ink droplet is not generated and ejected through nozzles of an imaging device unless it is needed to be placed on the recording medium.
Since drop-on-demand ink jet systems require no ink recovery, charging, or deflection operations, the system is simpler than the continuous stream ink jet system. There are three types of drop-on-demand ink jet systems. One type of drop-on-demand ink jet system has an ink filled channel or passageway having a nozzle on one end and a regulated piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer may prevent close spacing of nozzles necessary for high resolution printing, and physical limitations of the transducer in some cases can result in low ink drop velocity. Low drop velocity may seriously diminish tolerances for drop velocity variation and misdirectionality, thus impacting the system's ability to produce high quality copies, and also decreases printing speed. Drop-on-demand system which uses relatively large piezoelectric devices to eject the ink droplets may also suffer the disadvantage of a low resolution. However, better print quality and resolution can be obtained by using smaller piezoelectric devices and nozzle sizes. A second type of drop-on-demand ink jet device is known as acoustic ink jet printing which can be operated at high frequency and high resolution. The printing utilizes a focused acoustic beam formed with a spherical lens which projects a plane wave of sound created by a piezoelectric transducer. The focused acoustic beam reflected from a surface exerts a pressure on the surface of the liquid, resulting in ejection of small droplets of ink onto imaging substrate. Aqueous inks and hot melt inks can be used in this system.
The third type of drop-on-demand system is known as thermal ink jet or bubble jet printing, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information generate an electric current pulse in a resistive layer (resistor) within each ink passageway near the orifice of nozzle, causing the ink in the immediate vicinity of the resistor to be heated up periodically. Momentary heating of the ink leads to its evaporation almost instantaneously with the creation of a bubble. The ink at the orifice is forced out of the orifice as a propelled droplet at high speed as the bubble expands. When the hydrodynamic motion of the ink stops after discontinuous heating followed by cooling, the subsequent ink emitting process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provides simpler, low cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the thermal ink jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble nucleation and formation of around 280.degree. C. and above. Once nucleated and expanded, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. The bubble expands rapidly due to pressure increase upon heating until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle located either directly above or on the side of a heater, and once the excess of heat is removed with diminishing pressure, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has been terminated and, concurrently with bubble collapse, the droplet is propelled at a high speed in a direction toward a record medium or print substrate. Subsequently, the ink channel refills by a capillary action and is ready for the next repeating thermal ink jet printing process. The entire bubble formation and collapse sequences occurs in about 30 microseconds. The heater can be reheated to eject ink out of channel after about 60 to 2000 microseconds minimum dwell time and to enable the channel to be refilled with ink without causing dynamic refilling problem. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, U.S. Pat. No. 4,463,359, U.S. Pat. No. 4,532,530, U.S. Pat. No. 5,281,261, U.S. Pat. No. 5,139,574, and U.S. Pat. No. 5,145,518, the contents of which are hereby incorporated by reference.
Ink jet printing is a non-impact method that are deposited on a print substrate (substrate) such as plain paper or coated paper or textile cloth or transparent film in response to an electronic digital signal. Thermal or bubble jet ink jet printers which are operated in a drop-on-demand mode have found broad applications in digital printers, plotters, and fax machines as output for personal computers and large computer in the office and the home.
In an ink jet printing apparatus, the printhead typically comprises a linear array of ejectors containing resistors and orifices (or nozzles), and the printhead is moved relative to the surface of the print substrate (print sheet or recording medium), either by moving the print substrate relative to a stationary printhead, or vice versa, or both. In some types of apparatus, a relatively small printhead or an array of printhead comprising two or more small butted printheads in a partial-width printer moves across a print substrate (sheet) numerous time in swaths, much like a typewriter. The ink-jet apparatus of a printer disperses ink through the printhead onto a surface of a print substrate (e.g., paper) to form an image. Alternatively, a printhead, which consists of an array of nozzles and ejectors and extends the full width of the print substrate, may pass ink down the print substrate (sheet) one line at a time before the print substrate is advanced to complete the production of full-page images in what is known as a "full-width array" (FWA) ink jet printer. When the printhead and the print substrate are moved relative to each other, imagewise digital data is used to selectively activate the thermal energy generators (resistors) in the printhead over time so that the desired image will be created on the print substrate by depositing ink at a fast speed. However, at this time the use of partial-width printheads and full-width array printheads has not been shown in the commercial ink jet printers.
Some ink jet printers such as a desk top printer employ mobile printheads. A mobile printhead typically comprises a plurality of closely arranged nozzles provided in a small printing area. Such a mobile printhead produces partial digital images (e.g. checkerboard printing method), which when combined form large recognizable images, by sliding along a guide and dispersing ink during each "pass" across a print substrate (substrate). This type of ink jet printer usually is a slow speed desk top ink jet printer which is available in the current market. The mobile printhead may also comprise two or more butted printheads (i.e. a partial-width printhead with increasing number of ink nozzles; For example, it can comprise more than 384 nozzles per printhead such as the one employed in a partial-width array ink jet printer so that more ink can be delivered to a substrate in a single swath as the it moves across the print substrate. This type of partial-width ink jet printer will have a higher ink jet printing speed as compared to the aforementioned desk top ink jet printer with a single printhead per ink cartridge. In a multi-color ink jet printer, several printheads (e.g. black, cyan, magenta, and yellow) and their corresponding inks can be mounted in an ink jet assembly on a printhead holder and moved across the print substrate. Different color inks are dispersed onto a print substrate when they are moved relative to the print substrate or vice versa. Multi-color image can be obtained by repeated printing.
Other faster ink jet printer such as a single pass ink jet printer or full-width array ink printer employs a full-width array printhead comprising a plurality of closely arranged nozzles and ejectors arranged across a width of a print substrate(an array of butted printheads extended to the width of a print substrate; for example, it can comprise more than several thousand ink nozzles per printhead). These nozzles can disperse ink without time-consuming passes of the printhead across the print substrate. After a printhead has completed each print line on a print substrate, the printer advances the part of the print substrate allowing the next print line to be printed. Many known ink jet printheads and their applications were described in U.S. Pat. No. 5,057,854 issued to Pond et al on Oct. 15, 1991; U.S. Pat. No. 4,985,710 issued to Drake et al on Jan. 15, 1991; U.S. Pat. No. 5,098,503 issued to Drake on Mar. 24, 1992; U.S. Pat. No. 5,192,959 issued to Drake et al on Mar. 9, 1993; and U.S. Pat. No. 5,432,539 issued to Anderson on Sep. 30, 1995. The contents of these patents are hereby incorporated by reference.
In ink jet printing, sharp images can be obtained by using a high resolution printhead. The image resolution is related to the nozzle (orifice) size of an ink jet printhead. With the demand for higher resolution printers, the nozzles of a printhead or partial-width printhead or full-width printhead in ink jet printers are decreasing in size. Nozzle openings are typically about 50 to 80 micrometers in width or diameter for 300 spots per inch (spi) resolution printers. With the advent of higher resolution (e.g. 400 spi, and 600 spi) ink jet printers, these nozzle openings are typically about 10 to about 49 micrometers in width or diameter. A 600 spi printhead in an ink jet printer may have a nozzle size of less than 30 microns. At the present time, all commercial color thermal ink jet printers use only low resolution color ink jet printheads (i.e. .ltoreq.360 spi).
Ink jet printers can use various types of inks, each possessing different characteristics. For example, slow-drying inks have relatively high surface tensions (.gtoreq.45 dyne/cm) and long drying times, but produce high quality images with sharp edges and lines. many black inks including those dye-based and pigment-based black inks (e.g. carbon black inks) are preferred to be slow-drying inks. In contrast, fast-drying inks have relatively low surface tension (&lt;45 dyne/cm) and short drying times, but do not produce very high quality images like those slow-drying inks. For example, images formed using fast-drying inks may tend to "feather" when drying; that is, the ink laterally spreads out quickly while being absorbed by the plain paper, sometime resulting in rough edges. However, they are capable of printing a print substrate (paper) at a fast speed without serious smearing problem. Many color ink jet inks are fast-drying inks.
Examples of inks used in ink jet printers were described in U.S. Pat. No. 5,281,261 issued to Lin on Jan. 25, 199; U.S. Pat. No. 5,531,818 issued to Lin on Jul. 2, 1996; U.S. Pat. No. 5,139,574, issued to Winnik et al. on Aug. 18, 1992; U.S. Pat. No. 5,242,489, issued to Schwarz on Sep. 7, 1993; U.S. Pat. No. 5,254,158, issued to Breton et al. on Oct. 19, 1993; U.S. Pat. No. 5,258,064, issued to Colt on Nov. 2, 1993; and U.S. Pat. No. 5,340,388, issued to Breton et al. on Aug. 23, 1994. The contents of these patents are hereby incorporated by reference.
One problem with documents produced by ink jet printers is that, before drying, ink dispersed onto print substrates are subject to smearing. In particular, ink dispersed by a printhead initially lies on the paper surface before penetrating the substrate. While on the surface, the ink can be smeared by, for example, contact with part of the printer(e.g. printhead, roller, etc.) as the substrate is advanced. This is particularly true for the slow-drying inks and limited the speed of ink jet printing. While fast-drying inks are available, as discussed above, such inks can result in lower print quality as compared to slow-drying inks due to, for example, uncontrolled ink spreading and feathering on some plain papers. Thus, there is a need to avoid ink smearing and feathering on print substrates and to obtain high quality images.
Many ink jet printers produce multi-color images or documents by dispersing different colored inks(e.g. black, cyan, magenta, and yellow inks) onto print substrates. For example, a color document may have several different regions which are formed using different colored inks. However, during or before drying, a colored ink (first ink) from one region may move laterally into an adjacent region and mix with another colored ink (e.g. second ink, third ink, fourth ink, etc.) placed in the neighboring region. This mixing of different inks near the border area, commonly referred to as "intercolor bleeding", results in undesirable print degradation along the border of the regions with reducing print quality. Slow-drying inks tend to have a more severe intercolor bleeding problem on plain papers than the fast-drying inks. Thus, it is desirable to avoid intercolor bleeding in color documents produced by an ink jet printer.
Various techniques for ink drying have been proposed without dealing an intercolor bleeding problem associated with a multi-color ink jet printing process. For example, microwave devices are employed in one technique described in U.S. Pat. No. 5,220,346, issued to Carreira et al. on Jun. 15, 1993. The ink is printed on a substrate followed by microwave drying to give final print product. However, this technique does not mention about multi-color ink jet printing and its problem of intercolor bleeding. The intercolor bleeding is a very serious problem for a multi-color ink jet printing process especially when an ink set comprising at least a slow-drying ink(e.g. black ink) and three color inks (e.g. cyan, magenta, and yellow inks) of either a slow-drying type (ink jet inks with a surface tension.gtoreq.45 dyne/cm at room temperature) or fast-drying type (ink jet inks with a surface tension&lt;45 dyne/cm at room temperature). If the neighboring images of different color inks on the print substrate are not dried properly at room temperature or they are exposed to microwave radiation only after different inks have been deposited onto the substrate, intercolor bleeding may occur. The intercolor bleeding between two neighboring inks consisting of at least a slow-drying inks occurs very fast. It may take place so quickly that even before the images on a print substrate can be dried by a heater or a microwave device. The intercolor bleeding is a common problem for a multi-color ink jet printing (including the multi-pass ink jet printing to complete a line image) without heat (or dryer) assistance such as the ones observed in many commercial desk-top ink jet printers. The intercolor bleeding problem is even more severe in a fast speed single pass ink jet printing(such as the full-width array ink jet printing) than a slow speed multi-pass ink jet printing process which is commonly used in many commercial desk-top ink jet printers. This is because the fast speed ink jet printing does not allow adequate time for the high quality slow-drying ink(e.g. a slow-drying black ink) to dry on a print substrate before the deposition of another ink next to it. The mixing of two different color inks near the border of each other causes severe intercolor bleeding with poor image quality. As a consequence, a fast speed multi-color ink jet printing process involving a slow-drying ink (e.g. first ink, such as a black ink) and another ink (e.g. a second ink, such as a cyan or magenta or yellow ink, etc.) has severe intercolor bleeding and poor image quality problem. Thus, there is a need to develop a fast speed multi-color ink jet printing process to achieve high quality color images on plain papers.
In accordance with another drying technique, a print substrate is heated before ink is placed thereon (preheating a substrate). In this way, moisture in the print substrate is removed by evaporation, allowing the print substrate to better absorb the ink. Also, when ink is deposited onto the print substrate surface, heat from the print substrate reduces the ink's viscosity and facilitates movement of the ink into the print substrate. This technique alone improves ink drying slightly, however, it does not completely avoid intercolor bleeding especially in a fast ink jet printing process(e.g. at least greater than 5 pages per minute for a multiple color image)for multi-color ink jet printing. In many cases, the print substrate must be heated to a very high temperature even in a slow speed ink jet printing in order to avoid intercolor bleeding. There is a need for a multi-color ink jet printing at low temperature to avoid intercolor bleeding and smear.
Yet another technique provides delay times between dispersing different colored inks, so that an earlier deposited colored ink (first ink) has enough time to dry before other neighboring colored inks(e.g. second ink, third ink, and fourth ink) are subsequently deposited, thereby avoiding intercolor bleeding. For example, an ink jet printing technique referred to as "checkerboarding or checkerboard printing" whereby ink is dispersed intermittently during each pass of the printhead(s), so that multiple passes of the printhead(s) are required to form a complete print line. Long delay time is needed between printing two different color inks to obtain high quality image and it slows down the printing speed drastically making this printing process undesirable for a fast speed multi-color ink jet printer(e.g. .gtoreq.5 pages per minute for multiple color images). This method alone, however, does not accelerate the drying of inks for the printing and significantly limits the output of the ink jet printing.